Control apparatus and control method for internal combustion engine

ABSTRACT

An ECU executes a program including the steps of detecting the crank angle, advancing, at a crank angle at which the cam torque is exerted in the direction opposite to the rotational direction of an intake camshaft, the phase in which the intake valve is closed and retarding, at a crank angle at which the cam torque is exerted in the rotational direction of the intake camshaft, the phase in which the intake valve is closed.

This nonprovisional application is based on Japanese Patent ApplicationNo. 2005-318509 filed with the Japan Patent Office on Nov. 1, 2005, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to control of an internal combustionengine. In particular, the invention relates to the technique ofadvancing or retarding a phase in which a valve is closed, according toa torque exerted on a camshaft that drives the valve.

2. Description of the Background Art

An internal combustion engine has been known that has such valves asintake valves and exhaust valves opened and closed by rotation ofcamshafts. In such an internal combustion engine, as the camshaftrotates, a reaction force from the valve causes a torque acting on thecamshaft (the torque is also referred to as cam torque hereinafter). Asthe valve is opened, the cam torque is exerted in the direction oppositeto the rotational direction of the camshaft (the cam torque is exertedin the direction that hinders rotation of the camshaft). In contrast, asthe valve is closed, the cam torque is exerted in the rotationaldirection of the camshaft (the cam torque is exerted in the directionthat helps rotation of the camshaft). Therefore, the torque necessaryfor rotating the camshaft may vary to a significant degree while thecamshaft makes one rotation. Thus, for VVT (Variable Valve Timing) thatchanges the phase in which the valve is opened/closed (valveopening/closing timing) by rotation of the camshaft that drives thevalve (relative rotation with respect to the sprocket for example), thecam torque could influence the VVT. In other words, depending on thedirection in which the cam torque is exerted, the phase of the valve maybe easy to change or difficult to change by rotation of the camshaft.Therefore, it is necessary to take the cam torque into account forcontrolling the phase.

Japanese Patent Laying-Open No. 2005-076518 discloses a controlapparatus for a variable valve timing mechanism that changes the phaseaccording to the cam torque. The control apparatus disclosed in JapanesePatent Laying-Open No. 2005-076518 controls the variable valve timingmechanism that changes the rotational phase of the camshaft relative tothe crankshaft of the internal combustion engine to vary the valvetiming of an intake valve or an exhaust valve. The control apparatusdetects the state of the cam torque generated on the camshaft due tooperation of the cam driving to open/close the intake valve or theexhaust valve and, when the cam torque is generated in the directionopposite to the direction of changing the rotational phase, decreasesthe degree of change in rotational phase or maintains the rotationalphase as it is.

Regarding the control apparatus for the variable valve timing mechanismdisclosed in the above-referenced publication, when the rotational phaseis to be changed and the cam torque is generated in the direction thathinders the change of the rotational phase, the change (degree ofchange) of the rotational phase is decreased or the change in rotationalphase is stopped. Thus, an increase in engine load due to the cam torquecan be prevented.

As for a V-type 8-cylinder internal combustion engine employing adouble-plane (also referred to as dual-plane) crankshaft with crankpinsarranged at 90° therebetween, it is known that the right and left bankscannot be fired alternately and firing is successively caused in one ofthe banks. In such a V8 internal combustion engine, the cylinders arenot fired at regular intervals. Thus, valves provided to respectivecylinders have respective phases (opening/closing timings) that are notat regular intervals as well. Therefore, there may be the case where avalve of one of the cylinders is closed in a certain phase (at a certaintiming) while opening operation of another cylinder in the same bank maybe started in that phase (at that timing) and there may be the casewhere the above-described valve state does not occur. Accordingly, in aphase (at a timing) in (at) which valves of some of the cylinders areclosed, the cam torque exerted in the direction opposite to the camshaftrotational direction increases. If the cam torque exerted in thedirection opposite to the camshaft rotational direction is large, thephase in which the valve is actually closed is later than or delayedrelative to a phase determined under control due to influences ofdeformation or the like of such components as a chain coupling thecrankshaft and camshafts and other parts. In contrast, there may be thecase where the intake valve of any cylinder is closed in a certain phasewhile the intake valve of another cylinder in the same bank is in thetransition from the opening operation to the closing operation in thatphase and there may be the case where such a valve state does not occur.Accordingly, in a phase in which some of the cylinders are closed, thecam torque exerted in the camshaft rotational direction increases. Ifthe cam torque exerted in the camshaft rotational direction is large,the phase in which the valve is actually closed is earlier than oradvanced relative to a phase determined under control, due to influencesof deformation or the like of such components as the chain coupling thecrankshaft and camshafts and other parts. In the cylinder having itsintake valve closed in the delayed phase, the quantity of air pushedback from the cylinder into the intake manifold as the piston is liftedincreases, resulting in a decrease in final quantity of air sucked intothe cylinders. On the contrary, in the cylinder having its intake valveclosed in the advanced phase, the quantity of air pushed back from thecylinder into the intake manifold as the piston is lifted decreases,resulting in an increase in final quantity of air sucked into thecylinder. Therefore, some cylinders are smaller in sucked or intake airquantity than other cylinders. Further, in a cylinder having its exhaustvalve closed in a delayed phase, the quantity of exhaust gas sucked backfrom the exhaust manifold into the cylinder as the piston is moveddownward increases (namely internal EGR (Exhaust Gas Recirculation)quantity increases). On the contrary, in a cylinder having its exhaustvalve closed in an advanced phase, the quantity of exhaust gas suckedback from the exhaust manifold into the cylinder as the piston is moveddownward decreases. Therefore, the cylinders are nonuniform in internalEGR quantity. For such an internal combustion engine as described above,if the control apparatus for the variable valve timing mechanismdisclosed in Japanese Patent Laying-Open No. 2005-076518 is used, thedifference in quantity of air taken into cylinders as well as thedifference in internal EGR quantity could be increased. In other words,for such a cylinder having its intake valve or exhaust valve closed in adelayed phase, in the phase in which the intake valve or exhaust valveis closed, the cam torque is exerted in the direction opposite to thedirection in which the phase is advanced (camshaft rotationaldirection), so that advance of the phase is restrained or stopped. Onthe contrary, in such a cylinder having its intake valve or exhaustvalve closed in an advanced phase, in the phase in which the intakevalve or exhaust valve is closed, the cam torque is exerted in thedirection of advancing the phase, so that the advance of the phase iscontinued. Consequently, the phase in which the intake valve or exhaustvalve is actually closed is further displaced from a phase determinedunder control, which could increase differences in air quantity andinternal EGR for example between cylinders.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a control apparatus orthe like for an internal combustion engine that can restrain occurrenceof nonuniformity of cylinders with respect to each other in terms ofintake air quantity and internal EGR quantity.

A control apparatus for an internal combustion engine according to thepresent invention controls the internal combustion engine including acamshaft driving a valve and a change mechanism changing a phase inwhich the valve is closed. The control apparatus includes an operationunit. The operation unit controls the change mechanism in a manner thatthe phase is advanced in a case where a torque exerted on the camshaftby rotation of the camshaft acts in a direction opposite to a rotationaldirection of the camshaft, and controls the change mechanism in a mannerthat the phase is retarded in a case where the torque acts in therotational direction of the camshaft.

In accordance with the present invention, in the case where the torqueacts in the opposite direction to the camshaft rotational direction, thephase in which the valve is closed is advanced and, in the case wherethe torque acts in the camshaft rotational direction, the phase isretarded. Thus, for a cylinder, in the case where the torque acting inthe opposite direction to the camshaft rotational direction could causedelay of the phase (timing) in (at) which the intake valve or exhaustvalve is closed, the phase in which the intake valve or exhaust valve isclosed can be advanced. Accordingly, occurrence of delay of the phase inwhich the intake valve or exhaust valve is closed can be restrained.Further, for a cylinder, in the case where the torque acting in thecamshaft rotational direction could cause advance of the phase in whichthe intake valve or exhaust valve is closed, the phase in which theintake or exhaust valve is closed can be retarded. Accordingly,occurrence of advance of the phase in which the intake valve or exhaustvalve is closed can be restrained. Thus, the control apparatus for theinternal combustion engine can be provided that can restrain occurrenceof displacement of the phase in which the intake valve or exhaust valveof each cylinder is actually closed with respect to a phase determinedunder control, and can restrain occurrence of nonuniformity of cylinderswith respect to each other in terms of quantity of air taken into thecylinder and internal EGR quantity.

Preferably, the operation unit controls the change mechanism in a mannerthat the phase is advanced to a greater extent as the torque acting inthe direction opposite to the rotational direction of the camshaft islarger, and controls the change mechanism in a manner that the phase isretarded to a greater extent as the torque acting in the rotationaldirection of the camshaft is larger.

In accordance with the present invention, as the torque acting in theopposite direction to the camshaft rotational direction is larger, thephase of the intake valve or exhaust valve is advanced to a greaterextent. Further, as the torque acting in the camshaft rotationaldirection is larger, the phase of the intake valve or the exhaust valveis retarded to a grater extent. Accordingly, as delay in phase in whichthe intake valve or exhaust valve is closed is larger, the phase inwhich the intake valve or exhaust valve is closed can be advanced to agreater extent. Further, as advance in phase in which the intake valveor exhaust valve is closed is larger, the phase in which the intakevalve or exhaust valve is closed can be retarded to a greater extent.Thus, for each cylinder, occurrence of displacement of the phase inwhich the intake valve or exhaust valve is actually closed with respectto a phase determined under control can be restrained, and occurrence ofnonuniformity of cylinders with respect to each other in terms of intakeair quantity and internal EGR quantity can be restrained.

Still preferably, the operation unit controls the change mechanism in amanner that the phase is advanced to a greater extent as the camshafthas a higher rotational speed, and controls the change mechanism in amanner that the phase is retarded to a greater extent as the camshafthas a higher rotational speed.

In accordance with the present invention, as a higher camshaftrotational speed causes a larger torque acting in the opposite directionto the camshaft rotational direction, the phase of the intake valve orexhaust valve is advanced to a greater extent. Further, as a highercamshaft rotational speed causes a larger torque acting in the camshaftrotational direction, the phase of the intake valve or exhaust valve isretarded to a greater extent. Accordingly, as delay in phase in whichthe intake valve or exhaust valve is closed is larger, the phase inwhich the intake valve or exhaust valve is closed can be advanced to agreater extent. Further, as advance in phase in which the intake valveor exhaust valve is closed is larger, the phase in which the intakevalve or exhaust valve is closed can be retarded to a greater extent.Thus, for each cylinder, occurrence of displacement of the phase inwhich the intake valve or exhaust valve is actually closed with respectto a phase determined under control can be restrained, and occurrence ofnonuniformity of cylinders with respect to each other in terms of intakeair quantity and internal EGR quantity can be restrained.

Still preferably, the operation unit controls the change mechanism in amanner that the phase is advanced to a greater extent as the internalcombustion engine has a higher load, and controls the change mechanismin a manner that the phase is retarded to a greater extent as theinternal combustion engine has a higher load.

In accordance with the present invention, as a higher load of theinternal combustion engine causes a larger torque acting in the oppositedirection to the camshaft rotational direction, the phase of the intakevalve or exhaust valve is advanced to a greater extent. Further, as ahigher load of the internal combustion engine causes a larger torqueacting in the camshaft rotational direction, the phase in which theintake valve or exhaust valve is closed can be retarded to a greaterextent. Accordingly, as delay in phase in which the intake valve orexhaust valve is closed is larger, the phase in which the intake valveor exhaust valve is closed can be advanced to a greater extent. Further,as advance in phase in which the intake valve or exhaust valve is closedis larger, the phase in which the intake valve or exhaust valve isclosed can be retarded to a greater extent. Thus, for each cylinder,occurrence of displacement of the phase in which the intake valve orexhaust valve is actually closed with respect to a phase determinedunder control can be restrained, and nonuniformity of cylinders withrespect to each other in terms of intake air quantity and internal EGRquantity can be restrained.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a configuration of an engine of a vehicle onwhich an ECU is mounted that is a control apparatus according to anembodiment of the present invention.

FIG. 2 is a map defining target values of the phase of an intakecamshaft.

FIG. 3 is a perspective view showing a cylinder block.

FIG. 4 is a table showing the firing order of the engine.

FIG. 5 shows changes of a cam torque exerted on the intake camshaft.

FIG. 6 shows a map for correcting the phase of an intake valve.

FIG. 7 is a flowchart showing a control structure of a program executedby the ECU in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, embodiments of the present invention arehereinafter described. In the following description, like components aredenoted by like reference characters. They are also named identicallyand function identically. Therefore, a detailed description thereof isnot repeated.

Referring to FIG. 1, a description is given of an engine of a vehicle onwhich a control apparatus is mounted, according to an embodiment of thepresent invention. The control apparatus in the present embodiment isimplemented for example by means of a program executed by an ECU(Electronic Control Unit) 4000 shown in FIG. 1.

Engine 1000 is a V-type 8-cylinder engine having an “A” bank 1010 and a“B” bank 1012 each including a group of four cylinders. Here, any engineother than the V8 engine may be used.

Into engine 1000, air is sucked from an air cleaner 1020. The quantityof sucked air is adjusted by a throttle valve 1030. Throttle valve 1030is an electronic throttle valve driven by a motor.

The air is mixed with fuel in a cylinder 1040 (combustion chamber). Intocylinder 1040, the fuel is directly injected from an injector 1050. Inother words, injection holes of injector 1050 are provided withincylinder 1040.

The fuel is injected in the intake stroke. The fuel injection timing isnot limited to the intake stroke. Further, in the present embodiment,engine 1000 is described as a direct-injection engine having injectionholes of injector 1050 that are provided within cylinder 1040. However,in addition to direct-injection (in-cylinder) injector 1050, a portinjector may be provided. Moreover, only the port injector may beprovided.

The air-fuel mixture in cylinder 1040 is ignited by a spark plug 1060and accordingly burned. The air-fuel mixture after burned, namelyexhaust gas, is cleaned by a three-way catalyst 1070 and thereafterdischarged to the outside of the vehicle. The air-fuel mixture is burnedto press down a piston 1080 and thereby rotate a crankshaft 1090.

At the top of cylinder 1040, an intake valve 1100 and an exhaust valve1110 are provided. Intake valve 1100 is driven by an intake camshaft1120. Exhaust valve 1110 is driven by an exhaust camshaft 1130. Intakecamshaft 1120 and exhaust camshaft 1130 are coupled by such parts as achain and gears to be rotated at the same rotational speed.

Intake valve 1100 has its phase (opening/closing timing) controlled byan intake VVT mechanism 2000 provided to intake camshaft 1120. Exhaustvalve 1110 has its phase (opening/closing timing) controlled by anexhaust VVT mechanism 3000 provided to exhaust camshaft 1130.

In the present embodiment, intake camshaft 1120 and exhaust camshaft1130 are rotated by the VVT mechanisms to control respective phases ofintake valve 1100 and exhaust valve 1110. It is noted that the method ofcontrolling the phase is not limited to the aforementioned one.

Intake VVT mechanism 2000 is operated by an electric motor. Exhaust VVTmechanism 3000 is hydraulically operated. It is noted that intake VVTmechanism 2000 may be hydraulically operated while exhaust VVT mechanism3000 may be driven by an electric motor. Further, since any well-knownart may be applied to implement the VVT mechanism, a detaileddescription thereof is not given here.

To ECU 4000, signals indicating the rotational speed and the crank angleof crankshaft 1090 are input from a crank angle sensor 5000. Further, toECU 4000, signals indicating respective phases of intake camshaft 1120and exhaust camshaft 1130 (phase: the camshaft position in therotational direction) are input from a cam position sensor 5010.

Furthermore, to ECU 4000, a signal indicating the water temperature(coolant temperature) of engine 1000 from a coolant temperature sensor5020 as well as a signal indicating the quantity of intake air (quantityof air taken or sucked into engine 1000) of engine 1000 from an airflowmeter 5030 are input.

Based on these signals input from the sensors as well as a map and aprogram stored in a memory (not shown), ECU 4000 controls the throttleopening position, the ignition timing, the fuel injection timing, thequantity of injected fuel, the phase of intake valve 1100 and the phaseof exhaust valve 1110 for example, so that engine 1000 is operated in adesired operating state.

In the present embodiment, ECU 4000 determines the phase of intake valve1100 based on the map as shown in FIG. 2 that uses the engine speed NEand the intake air quantity KL as parameters. A plurality of maps forrespective coolant temperatures are stored for determining the phase ofintake valve 1100.

Referring to FIG. 3, a further description of engine 1000 is given. In“B” bank 1012 of a cylinder block 1002 of engine 1000, cylinders 1040 towhich respective numbers #1, #3, #5 and #7 are allocated are formed andarranged successively from the front side to the rear side of thevehicle.

Further, in “A” bank 1010 of cylinder block 1002, cylinders 1040 towhich respective numbers #2, #4, #6 and #8 are allocated are formed andarranged successively from the front side to the rear side of thevehicle.

As shown in FIG. 4, firing is caused in the cylinders in the order of #1cylinder, #8 cylinder, #7 cylinder, #3 cylinder, #6 cylinder, #5cylinder, #4 cylinder, and #2 cylinder. The firing interval is 90° incrank angle (CA).

While crankshaft 1090 makes two rotations (720° in crank angle), onecycle of engine 1000 is completed that is comprised of the four steps:intake stroke→compression stroke→power stroke→exhaust stroke. Therefore,between two cylinders one of which precedes the other with anothercylinder therebetween in firing order, namely between two cylinders at afiring interval of 180° in crank angle, there is a difference in cyclecorresponding to one stroke in the cycle.

Thus, when #1 cylinder is in the transition from the intake stroke tothe compression stroke, #7 cylinder is in the transition from theexhaust stroke to the intake stroke. Here, in the phase (timing) inwhich intake valve 1100 of #1 cylinder is closed, intake valve 1100 of#7 cylinder starts opening operation. Therefore, the cam torqueincreases that is exerted in the direction opposite to the direction inwhich intake camshaft 1120 rotates.

The cam torque exerted in the direction opposite to the rotationaldirection of intake camshaft 1120 increases in the phase in which intakevalve 1100 of #3 cylinder is closed, in addition to the phase in whichintake valve 1100 of #1 cylinder is closed.

Further, regarding two cylinders that are successive in firing order,namely two cylinders at a firing interval of 90° in crank angle, in thephase in which intake valve 1100 of one cylinder preceding in firingorder is closed, intake valve 1100 of the other cylinder following infiring order is in the transition from the opening operation to theclosing operation.

In the present embodiment, in the phase in which intake valve 1100 of #7cylinder is closed, intake valve 1100 of #3 cylinder is in thetransition from the opening operation to the closing operation.Therefore, the cam torque exerted in the direction in which intakecamshaft 1120 is rotated increases.

A similar state to the above-described one may also occur in “A” bank1010. As shown in FIG. 5, in the phase in which respective intake valves1100 of #2 cylinder and #6 cylinder are closed, the cam torque exertedin the direction opposite to the rotational direction of intake camshaft1120 is larger. Further, in the phase in which intake valve 1100 of #4cylinder is closed, the cam torque exerted in the rotational directionof intake camshaft 1120 is larger.

It is noted that, in FIG. 5, the solid line represents the cam torqueexerted on intake camshaft 1120 provided to “B ” bank 1012. The brokenline represents the cam torque exerted on intake camshaft 1120 providedto “A” bank 1010. The dots each represent the cam torque at a crankangle at which intake valve 1100 of each cylinder 1040 is closed.

Moreover, in FIG. 5, the cam torque exerted in the direction opposite tothe rotational direction of intake camshaft 1120 is represented by apositive value and the cam torque exerted in the rotational direction ofintake camshaft 1120 is represented by a negative value.

If the cam torque exerted in the direction opposite to the rotationaldirection of intake camshaft 1120 is larger, the phase in which intakevalve 1100 is actually closed is later than a phase determined undercontrol, due to influences of deformation or the like of such componentsas the chain coupling the crankshaft and camshafts and other parts.Accordingly, the phase in which respective intake valves 1100 of #1cylinder, #3 cylinder, #2 cylinder and #6 cylinder are actually closedis later than the phase in which respective intake valves 1100 of othercylinders are closed.

On the contrary, if the cam torque exerted in the rotational directionof intake camshaft 1120 is larger, the phase in which intake valve 1100is actually closed is earlier than a phase determined under control, dueto influences of deformation or the like of such components as the chaincoupling the crankshaft and camshafts and other parts. Accordingly, thephase in which respective intake valves 1100 of #7 cylinder and #4cylinder are actually closed is earlier than the phase in whichrespective intake valves 1100 of other cylinders are closed.

In cylinder 1040 having intake valve 1100 closed in a phase as delayed,the quantity of air pushed back from cylinder 1040 into the intakemanifold as piston 1080 is lifted increases, resulting in a decrease infinal quantity of air sucked into cylinder 1040.

On the contrary, in cylinder 1040 having intake valve 1100 closed in aphase as advanced, the quantity of air pushed back from cylinder 1040into the intake manifold as piston 1080 is lifted decreases, resultingin an increase in final quantity of air sucked into cylinder 1040.

Thus, the cylinders differ from each other in intake air quantity. Inthis case, fluctuation of the rotation of crankshaft 1090 (fluctuationof the rotational speed while one rotation is made) increases, andaccordingly vibrations and noise of engine 1000 could increase.

Then, in the present embodiment, the phase in which intake valve 1100 isclosed is corrected so that the difference in quantity of air suckedinto cylinder 1040 is decreased as much as possible. The phase in whichintake valve 1100 is closed is corrected, as shown in FIG. 6, based onthe map defining, according to the cam torque, the extent to which thephase should be corrected.

The phase in which intake valve 1100 is closed is corrected, in the casewhere the crank angle is a crank angle at which the cam torque isexerted in the direction opposite to the rotational direction of intakecamshaft 1120, so that the phase is advanced relative to a referencephase defined by the map shown in FIG. 2 (the phase determined fromengine speed NE and intake air quantity KL).

In contrast, the phase in which intake valve 1100 is closed iscorrected, in the case where the crank angle is a crank angle at whichthe cam torque is exerted in the rotational direction of intake camshaft1120, so that the phase is retarded relative to the reference phasedefined by the map shown in FIG. 2.

Referring to FIG. 7, a description is given of a control structure of aprogram executed by ECU 4000 that is a control apparatus according tothe present embodiment.

In step (hereinafter step is abbreviated as S) 100, ECU 4000 detects thecrank angle based on a signal (pulse signal) transmitted from crankangle sensor 5000.

In S200, ECU 4000 corrects, based on the detected crank angle and theaforementioned map (see FIG. 6), the phase in which intake valve 1100 ofeach cylinder 1040 is closed to a phase that is advanced or retardedrelative to the reference phase. Intake VVT mechanism 2000 is controlledso that the corrected phase is implemented. After this, this process isended.

A description is given of an operation of ECU 4000 that is the controlapparatus in the present embodiment based on the above-describedstructure and flowchart.

While the engine is operating, the crank angle is detected (S 100) and,at a crank angle at which the cam torque is exerted in the directionopposite to the rotational direction of intake camshaft 1120, the phasein which intake valve 1100 is closed is advanced (S200).

Thus, in the case where the cam torque exerted in the direction oppositeto the rotational direction of intake camshaft 1120 could retard thephase in which intake valve 1100 is actually closed, the phase of intakevalve 1100 can be advanced. Accordingly, occurrence of delay in phase inwhich intake valve 1100 is actually closed can be restrained.

Further, at a crank angle at which the cam torque is exerted in therotational direction of intake camshaft 1120, the phase in which intakevalve 1100 is closed is retarded (S200). Thus, in the case where the camtorque exerted in the rotational direction of intake camshaft 1120 couldadvance the phase in which intake valve 1100 is actually closed, thephase of intake valve 1100 can be retarded. Accordingly, occurrence ofadvance in phase in which intake valve 1100 is actually closed can berestrained.

As discussed above, with the ECU identified as the control apparatus inthe present embodiment, at a crank angle at which the cam torque isexerted in the direction opposite to the rotational direction of theintake camshaft, the intake VVT mechanism is controlled so that thephase in which the intake valve is closed is advanced. Further, at acrank angle at which the cam torque is exerted in the rotationaldirection of the intake camshaft, the intake VVT mechanism is controlledso that the phase in which the intake valve is closed is retarded. Thus,for a cylinder, in the case where the cam torque exerted in thedirection opposite to the rotational direction of the intake camshaftcould retard the phase in which the intake valve of the cylinder isactually closed, the phase in which the intake valve is closed can beadvanced. Accordingly, occurrence of delay in phase in which the intakevalve is actually closed can be restrained. In contrast, for a cylinder,in the case where the cam torque exerted in the rotational direction ofthe camshaft could advance the phase in which the intake valve of thecylinder is actually closed, the phase in which the intake valve isclosed can be retarded. Accordingly, occurrence of advance in phase inwhich the intake valve is actually closed can be restrained. In thisway, occurrence of displacement can be restrained of the phase in whichthe intake valve of each cylinder is actually closed, with respect to aphase determined under control, and occurrence of nonuniformity ofcylinders with respect to each other in terms of quantity of air suckedinto the cylinder can be restrained.

Other Embodiments

In such cases where the rotational speed of intake camshaft 1120 is highand where the load of engine 1000 is high, namely the case where theabsolute value of the cam torque is relatively large, the extent towhich the phase is corrected may be larger than the one used in the casewhere the absolute value of the cam torque is relatively small. In otherwords, in the case where the cam torque exerted in the directionopposite to the direction in which intake camshaft 1120 is rotated isrelatively large, the phase in which intake valve 1100 is closed may beadvanced to a greater extent than the one used in the case where theaforementioned cam torque is relatively small. Further, in the casewhere the absolute value of the cam torque exerted in the rotationaldirection of intake camshaft 1120 is relatively large, the phase inwhich intake valve 1100 is closed may be retarded to a greater extentthan the one used in the case where the aforementioned absolute value isrelatively small.

In this way, as the phase in which intake valve 1100 is actually closedis delayed to a greater extent, the phase of intake valve 1100 may beadvanced to a greater extent. Further, as the phase in which intakevalve 1100 is actually closed is advanced to a greater extent, the phaseof intake valve 1100 may be retarded to a greater extent. Thus,occurrence of displacement of the phase in which the intake valve ofeach cylinder is actually closed with respect to a phase determinedunder control can be restrained, and occurrence of nonuniformity ofcylinders with respect to each other in terms of intake air quantity canbe restrained.

Furthermore, in addition to or instead of intake valve 1100, exhaustvalve 1110 may be advanced or retarded in phase according to the camtorque. This is because of the fact that a cylinder having exhaust valve1100 closed in a delayed phase has an increased internal EGR quantitywhile a cylinder having exhaust valve 1100 closed in an advanced phasehas a decreased internal EGR quantity, resulting in nonuniformity ofcylinders with respect to each other in internal EGR quantity andincreased rotational fluctuations of engine 1000.

Thus, for cylinder 1040, in the case where the cam torque exerted in thedirection opposite to the rotational direction of exhaust camshaft 1130could delay the phase in which exhaust valve 1110 is actually closed,the phase of exhaust valve 1110 can be advanced. Accordingly, occurrenceof delay of the phase in which exhaust valve 1110 is actually closed canbe restrained.

Further, for cylinder 1040, in the case where the cam torque exerted inthe rotational direction of exhaust camshaft 1130 could advance thephase in which exhaust valve 1110 is actually closed, the phase ofexhaust valve 1110 can be retarded. Accordingly, occurrence of advanceof the phase in which exhaust valve 1110 is actually closed can berestrained. Consequently, for each cylinder, occurrence of displacementof the phase in which exhaust valve 1110 is actually closed with respectto a phase determined under control can be restrained, and occurrence ofnonuniformity of cylinders with respect to each other in terms ofinternal EGR quantity can be restrained.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A control apparatus for an internal combustion engine including acamshaft driving a valve and a change mechanism changing a phase inwhich said valve is closed, said control apparatus comprising anoperation unit, and said operation unit controlling said changemechanism in a manner that the phase is advanced in a case where atorque exerted on said camshaft by rotation of said camshaft acts in adirection opposite to a rotational direction of said camshaft, andcontrolling said change mechanism in a manner that the phase is retardedin a case where said torque acts in the rotational direction of saidcamshaft.
 2. The control apparatus for the internal combustion engineaccording to claim 1, wherein said operation unit controls said changemechanism in a manner that the phase is advanced to a greater extent asthe torque acting in the direction opposite to the rotational directionof said camshaft is larger, and controls said change mechanism in amanner that the phase is retarded to a greater extent as the torqueacting in the rotational direction of said camshaft is larger.
 3. Thecontrol apparatus for the internal combustion engine according to claim1, wherein said operation unit controls said change mechanism in amanner that the phase is advanced to a greater extent as said camshafthas a higher rotational speed, and controls said change mechanism in amanner that the phase is retarded to a greater extent as said camshafthas a higher rotational speed.
 4. The control apparatus for the internalcombustion engine according to claim 1, wherein said operation unitcontrols said change mechanism in a manner that the phase is advanced toa greater extent as said internal combustion engine has a higher load,and controls said change mechanism in a manner that the phase isretarded to a greater extent as said internal combustion engine has ahigher load.
 5. A control method for an internal combustion engineincluding a camshaft driving a valve and a change mechanism changing aphase in which said valve is closed, comprising the steps of:controlling said change mechanism in a manner that the phase is advancedin a case where a torque exerted on said camshaft by rotation of saidcamshaft acts in a direction opposite to a rotational direction of saidcamshaft; and controlling said change mechanism in a manner that thephase is retarded in a case where said torque acts in the rotationaldirection of said camshaft.
 6. The control method for the internalcombustion engine according to claim 5, wherein said step of controllingsaid change mechanism in the manner that the phase is advanced includesthe step of controlling said change mechanism in a manner that the phaseis advanced to a greater extent as the torque acting in the directionopposite to the rotational direction of said camshaft is larger, andsaid step of controlling said change mechanism in the manner that thephase is retarded includes the step of controlling said change mechanismin a manner that the phase is retarded to a greater extent as the torqueacting in the rotational direction of said camshaft is larger.
 7. Thecontrol method for the internal combustion engine according to claim 5,wherein said step of controlling said change mechanism in the mannerthat the phase is advanced includes the step of controlling said changemechanism in a manner that the phase is advanced to a greater extent assaid camshaft has a higher rotational speed, and said step ofcontrolling said change mechanism in the manner that the phase isretarded includes the step of controlling said change mechanism in amanner that the phase is retarded to a greater extent as said camshafthas a higher rotational speed.
 8. The control method for the internalcombustion engine according to claim 5, wherein said step of controllingsaid change mechanism in the manner that the phase is advanced includesthe step of controlling said change mechanism in a manner that the phaseis advanced to a greater extent as said internal combustion engine has ahigher load, and said step of controlling said change mechanism in themanner that the phase is retarded includes the step of controlling saidchange mechanism in a manner that the phase is retarded to a greaterextent as said internal combustion engine has a higher load.
 9. Acontrol apparatus for an internal combustion engine including a camshaftdriving a valve and a change mechanism changing a phase in which saidvalve is closed, said control apparatus comprising: first control meansfor controlling said change mechanism in a manner that the phase isadvanced in a case where a torque exerted on said camshaft by rotationof said camshaft acts in a direction opposite to a rotational directionof said camshaft; and second control means for controlling said changemechanism in a manner that the phase is retarded in a case where saidtorque acts in the rotational direction of said camshaft.
 10. Thecontrol apparatus for the internal combustion engine according to claim9, wherein said first control means includes means for controlling saidchange mechanism in a manner that the phase is advanced to a greaterextent as the torque acting in the direction opposite to the rotationaldirection of said camshaft is larger, and said second control meansincludes means for controlling said change mechanism in a manner thatthe phase is retarded to a greater extent as the torque acting in therotational direction of said camshaft is larger.
 11. The controlapparatus for the internal combustion engine according to claim 9,wherein said first control means includes means for controlling saidchange mechanism in a manner that the phase is advanced to a greaterextent as said camshaft has a higher rotational speed, and said secondcontrol means includes means for controlling said change mechanism in amanner that the phase is retarded to a greater extent as said camshafthas a higher rotational speed.
 12. The control apparatus for theinternal combustion engine according to claim 9, wherein said firstcontrol means includes means for controlling said change mechanism in amanner that the phase is advanced to a greater extent as said internalcombustion engine has a higher load, and said second control meansincludes means for controlling said change mechanism in a manner thatthe phase is retarded to a greater extent as said internal combustionengine has a higher load.